1. Field of the Invention
The present invention relates to an ignition device for an internal combustion engine which integrally incorporates a spark plug and an ignition coil and also relates to a method for assembling this ignition device.
2. Description of the Background Art
There are various kinds of conventional ignition devices integrally incorporating a spark plug and an ignition coil, which are for example disclosed in Japanese Patent Application Laid-open No. 2000-252040, Japanese Patent Application Laid-open No. 2000-277232 and European Patent Application Laid-open No. 0907019.
However, the conventional ignition devices integrally incorporating a spark plug and an ignition coil are long in length and small in diameter. Therefore, these ignition devices have high internal stresses when subjected to severe heat and cool cycles. To avoid this, adding stress relaxing members is conventionally known to reduce the internal stresses and prevent generation of cracks. Increasing the thickness of an insulating resin layer is also conventionally known as being effective to reduce the stresses. However, these conventional techniques tend to be expensive in the costs required and there will be no substantial margin for actually realizable reduction in the diameter.
Furthermore, the conventional ignition coils were entirely hardened with an insulating resin, such as an epoxy resin or comparable thermosetting resin. Hence, after the ignition coil is once assembled as a finished product, disassembling the ignition coil into individual materials or original members was difficult or substantially impossible. In other words, recycling constituent components or parts of the conventional ignition coils was no practically realized.